Internal combustion engines including diesel engines produce a number of combustion products including particulates, hydrocarbons (“HC”), carbon monoxide (“CO”), oxides of nitrogen (“NOx”), oxides of sulfur (“SOx”) and others. Diesel particulate filters, such as catalyzed soot filters, close coupled catalysts, and others, can be used to trap particulates and reduce emissions from diesel exhaust.
In order to reduce the accumulation of particulate matter or soot on a filter, the filter is exposed to high temperatures by either increasing the engine load to increase temperature of the exhaust gas passing through the filter or by injecting fuel in the vicinity of the filter causing combustion. The combination of a catalyst and high temperature in the filter allows the accumulated soot to react with NO2, converting it to carbon dioxide and thereby regenerating the filter. Active and passive regeneration of particulate filters associated with mobile diesel engines is easily achieved due to the high operating temperatures during normal operation and the sophisticated control systems typically incorporated in mobile systems, such as those found in automobiles. However, the same may not be true of stationary diesel engines.
Soot accumulation occurs at low load or low operating temperatures of a diesel engine, such as during cold starts. This is particularly a problem for stationary diesel engines which are used for back-up power generation. Back-up generators are used infrequently and typically are oversized for the facility for which they supply power, so that should the facility expand, a replacement generator will not be needed to meet any increase in power demand. Therefore, such stationary diesel engines operate at low load and do not generate the high exhaust temperatures during normal operation needed for filter regeneration. Many local ordinances require the regular inspection of back-up generators to determine whether they are working properly. The inspection involves turning on the generator for a short period of time periodically to ensure that the generator is operational. Therefore, the regular maintenance of stationary generators demanded by local legislation also contributes to soot accumulation.